The present invention relates generally to electronic circuits, and more particularly to a capacitor for use in integrated circuits.
There is a continuing demand for integrated circuits to perform more functions or operations in shorter periods of time. This typically requires additional components to perform the additional functions, store more data and operate more efficiently. At the same time packaging requirements are decreasing. Consumers want smaller, lighter weight products that do more and are more mobile or portable. Accordingly, circuit designers are challenged to provide more components or greater capacity per unit of area on a semiconductor die. Most electronic circuits include basic electrical components such as transistors, resistors, inductors, capacitors and the like. Capacitors are one component that can occupy a lot of area on a semiconductor die depending upon the size of the capacitor. Capacitors are typically made by depositing a first metal plate, depositing a layer of insulation material over the first metal plate and then depositing a second metal plate over the layer of insulation material and parallel to the first metal plate. The size of the capacitance will be a function of the surface area of the two facing parallel plates and other parameters such as the dielectric constant of the insulation material and the spacing between the plates. Accordingly, one primary means of increasing the capacitance, is to increase the size of each of the parallel plates but this will consume more area on the semiconductor die.
Additionally, in some circuits it may be desirable for the capacitor to be independent of voltage and frequency applied across the capacitor once it is charged to a predetermined level. For example, a capacitor may be connected to the non-inverting input of an operational amplifier to reduce or cancel the offset voltage inherent in the operational amplifier. The capacitor may be pre-charged to the opposite polarity of the offset voltage of the amplifier so that the offset voltage is canceled during normal operation of the amplifier. When an input voltage signal is applied to the input of the operational amplifier, the output voltage signal will be stable and uninfluenced by the offset voltage if the capacitor is voltage and frequency independent.
Accordingly, for the reason stated above, and for other reasons that will become apparent upon reading and understanding the present specification, there is a need for a capacitor that maximizes the amount of capacitance per unit of area of a semiconductor die and that is independent of voltage and frequency.
In accordance with the present invention, a capacitor includes a layer of conductive material formed on a substrate or semiconductor die. The layer of conductive material includes a first portion and a second portion. The first and second portions are arranged in a predetermined pattern relative to one another to provide a maximum amount of capacitance per unit of area on the substrate or semiconductor die.
In accordance with one embodiment of the present invention, the first portion and the second portion of the layer of conductive material each have a substantially comb-like structure with a plurality of teeth. The teeth of the first portion and the teeth of the second portion are interleaved and each tooth includes a pair of sidewalls. Each sidewall, except an outside sidewall of an end tooth, faces a sidewall of a tooth of the other portion to provide a maximum of juxtaposed surface area.
In accordance with another embodiment of the present invention, an integrated circuit includes an amplifier formed on a substrate or semiconductor die and a capacitor formed on the substrate and connected to an input of the amplifier. The capacitor includes a first substantially comb-like structure of conductive material with a plurality of teeth and a second substantially comb-like structure of conductive material also with a plurality of teeth. The teeth of the second substantially comb-like structure are interleaved with the teeth of the first substantially comb-like structure and each tooth of the first and second comb-like structures have a pair of sidewalls. Each sidewall has a selected surface area and each of the teeth of the first and second comb-like structures are separated by a gap of a chosen width to provide a predetermined capacitance.
In accordance with another embodiment of the present invention, a memory system includes an array of memory elements. Each memory element is connected by one of plurality of row lines and by one of a plurality of column lines. An amplifier is connected to at least one of each of the plurality of column lines or each of the plurality of row lines. A capacitor is connected to an input of each amplifier to cancel the offset voltage of the amplifier. The capacitor includes a layer of conductive material having a first portion and a second portion. The first portion and the second portion are arranged in a predetermined pattern relative to one another to provide a maximum amount of capacitance per given area of the substrate or semiconductor die.
In accordance with a further embodiment of the present invention, a electronic system includes a processor and a memory device coupled to the processor. The memory device includes an array of memory elements and each memory element is connected by one of a plurality of row lines and by one of a plurality of column lines. An amplifier is connected to at least one of each of the plurality of row lines or to each of the plurality of column lines. A capacitor is connected to an input of each amplifier to cancel the offset voltage. Each capacitor includes a layer of conductive material divided into a first portion and a second portion. The first and second portions are arranged in a predetermined pattern relative to one another to provide a maximum amount of capacitance per given area of a substrate or semiconductor die.
In accordance with a further embodiment of the present invention, a method for making a capacitor includes depositing at least one layer of conductive material on a substrate; removing material from the layer of conductive material to form a first and second portion arranged in a predetermined pattern relative to one another to provide a maximum amount of capacitance per area of the substrate or wafer.
In accordance with another embodiment of the present invention, a method for correcting for offset voltage in an amplifier includes: connecting an output of the amplifier to an inverting input of the amplifier; connecting a capacitor between the inverting input and a positive or non-inverting input of the amplifier, wherein the capacitor comprises a layer of conductive material including at least a first portion and a second portion and wherein the first portion and the second portion are arranged in a predetermined pattern relative to one another to provide a maximum capacitance per area; and connecting the positive input of the amplifier to ground to cause the capacitor to charge to the offset voltage.
In accordance with a further embodiment of the present invention, a method for applying a stable voltage to a column or a row line of a memory device includes forming an amplifier and connecting an output of the amplifier to one of the row line or the column line; forming a capacitor connected to an input of the amplifier, wherein the capacitor is formed by depositing at least one layer of conductive material and removing material from the at least one layer of conductive material to form a first portion and a second portion that are arranged in a predetermined pattern relative to one another to provide a maximum capacitance per area of a semiconductor wafer or die; and forming circuitry to charge the capacitor to an opposite polarity of the offset voltage to nullify the offset voltage of the amplifier.